1. Field of the Invention
This invention relates to oil and gas production wells and particularly to methods of simultaneously removing asphaltene and/or paraffin and scale from such wells.
2. Description of the Prior Art
Paraffin and/or asphaltene and scale formation in producing oil wells, and particularly those wells producing high-paraffin containing oils, significantly interferes with the effectiveness and efficiency of the well production. In severe cases, the presence of paraffin and/or asphaltene and scale, can, in essence, cause the oil production for a given well to cease.
Generally, the paraffin and/or asphaltene crystallizes out of and solidifies in the well bore, the area surrounding the well bore, the casing and tubing of the well thereby blocking further production.
In the past, attempts have been made to remove the paraffin and/or asphaltene by mechanically cutting it out of the well or using a so-called “hot-oiling” technique. The cutting procedure is a relatively crude procedure and requires extensive well shutdown time. Moreover, it is extremely inefficient inasmuch as substantial amounts of paraffin and/or asphaltene remain in the well. This remaining paraffin and/or asphaltene provides seed crystals which promote the rapid formation of additional paraffin and/or asphaltene. Consequently, paraffin and/or asphaltene builds up and the blocking situation quickly occurs again.
In the hot-oiling method, produced crude is heated to a temperature well above the melting point of the paraffin and/or asphaltene and is then circulated down through the annulus of the well and returned to a hot-oil heating truck via the production tubing. The purpose here is for the hot oil to melt and/or dissolve the paraffin so that it can be removed from the well in liquid form. This is an expensive method since the crude must be put through a heater treater along with a demulsifier in order to facilitate the removal of solids and water therefrom. In this method, the crude oil used is taken from the stock tank and has thus already made one pass through the treating facility and has already been demulsified. Another disadvantage to this method is that in many instances, 100% of the fluid injected is not recovered and thus some is lost to the reservoir.
During the hot-oiling process, a paraffin dispersant which is based on a petroleum sulfonate is added to the crude as it is being heated. The paraffin dispersant assists in dispersing the melted paraffin in the hot-oil phase.
Moreover, this technique is very dangerous, particularly with wells producing a crude having a low flash point. Indeed, such wells cannot be hot-oiled because the auto-ignition temperature of the oil is so low. Thus, bringing the oil in direct contact with a heating mechanism creates a substantial fire hazard.
Another procedure that has been tried is the so-called “hot acid” technique. In this process, an attempt is made to melt paraffin using a combination of hot water, heated xylene and hot acid. However, while this mixture may have some effect on the removal of carbonate scale build-up in wells, it has not presented a satisfactory answer to paraffin and/or asphaltene removal.
An additional disadvantage of each of the above methods is due to the fact that normally it is desirable to subject a well to acidization at some subsequent point in time after the paraffin and/or asphaltene removal. The mechanical cutting technique, hot-acid technique, and the hot-oil techniques leave the well bore, the area surrounding the well bore casing and tubing “oil wet”. This is a disadvantageous situation for subsequent acidization. In the acidization technique, a mineral acid solution is introduced into the well to remove mineral deposits. The acid solution is aqueous and, if the interior portions and mechanical elements of the well are oil wet, direct contact of these surfaces with the acid solution is inhibited making the acidization treatment much less effective.
Such stimulation of oil and gas wells is a well known process and is described in U.S. Pat. No. 4,541,483.
Other more recent prior art attempts have been made trying to overcome the presence of the undesirable paraffin and/or asphaltene and scale in oil wells and associated equipment as stated below. In U.S. Pat. No. 3,930,539 there is disclosed a method for increasing the production in wells by the utilization of hydrochloric and phosphoric acid followed by ammonia to create a violent exothermic reaction at the bottom of the well and thus disintegrate the limestone and emulsify the paraffin thereby creating larger passages in the formation and which permits greater flow. This is not desirable since the reactions themselves create safety hazards and the paraffin still remains.
In U.S. Pat. No. 4,836,286, there is disclosed a method of removing flow-restricting matter such as paraffins from wells by use of a three stage process of introducing various solvent solutions into the bottom of the well over a period of time and then removing the solvents there from and passing an electrical charge there through followed by the reintroduction into the well. This has the disadvantage of numerous steps and the use of electrical charge.
In U.S. Pat. No. 6,593,279, there is disclosed the use of an acid based emulsion for cleaning oil sludges from well cuttings, well formations and down hole wells. These emulsions contain water, a surfactant mixture, an oil, a solvent, and an oxidizer. There is no disclosure of the removal of scale.
In U.S. Pat. No. 4,278,129, there is disclosed a two stage process of stimulating an oil well by the use of an oxyalkylated phosphate ester surfactant followed by the introduction of a hydrocarbon to drive the ester into the formation.
In U.S. Pat. No. 4,813,482, there is disclosed a method of removing paraffin from an oil well by treating the well with a heated solution containing a surfactant, a hydrocarbon solvent, and water in order to disperse the paraffin with the well into the solution.
In U.S. Pat. No. 5,909,774, there is disclosed a method of cleaning up a producing interval of a well bore drilled using a synthetic oil-water emulsion drill-in fluid. This method involves the use of three treatment fluids in three separate stages.
In U.S. Pat. No. 6,112,814, there is disclosed a method for cleaning a well bore plugged with deposits of heavy hydrocarbons and finely-divided inorganic solids by circulating a surfactant composition containing an alkyl polyglycoside, an ethoxylated alcohol, a caustic and an alkyl alcohol through the well bore with a coiled tubing.
The problems associated with the prior art set forth above are the use of numerous steps to remove paraffin, asphaltene, sludge, scale and/or other undesired materials from the wells and the fact that these multistep procedures are expensive and not efficient. These prior art problems are overcome by the unique one step method set forth below and the use of a novel aqueous cleaning emulsion which does not have to be heated to work over a wide range of temperatures.